1. Field of the Invention:
The present invention relates generally to position sensing apparatus and more particularly to magnetic effect sensing apparatus including linear position sensing as well as the commonly known rotary position xe2x80x9cgeartooth sensorsxe2x80x9d wherein a magnetically sensitive device senses a ferrous object or objects generally projecting from a rotating target and resembling the teeth of a gear.
2. Discussion of the Related Art:
Various sensors are known in the magnetic effect sensing arts. Examples of common magnetic effect sensors may include Hall effect and magnetoresistive technologies. Generally described, these magnetic sensors will respond to the change of magnetic field as influenced by the presence or absence of a ferromagnetic target object of a designed shape passing by the sensory field of the magnetic effect sensor. The sensor will then give an electrical output which can be further modified as necessary by subsequent electronics to yield sensing and control information. The subsequent electronics may be either onboard or outboard of the sensor package per se. In the following explanation the ordinarily skilled artisan will appreciate that adjacent slot and tooth combinations, in whatever order, are necessary to produce the duty cycle required for an intelligible output pulse. Thus, a reference to xe2x80x9cslot-to-toothxe2x80x99 may be deemed equivalent to xe2x80x9ctooth-to-slotxe2x80x9d, and the obvious or equivalent inverse will not be stated in the text where the two would simply be inversions of each other.
For example, geartooth sensors are known in the automotive arts to provide information to an engine controller for efficient operation of the internal combustion engine. One such known arrangement involves the placing of a ferrous target wheel on the crank shaft of the engine with the sensor located proximate thereto. The target objects, or features, i.e. tooth and slot, are of course properly keyed to mechanical operation of engine components. The regularly spaced tooth-to-slot transitions yield a rhythmic, or regular, pulse pattern which determines the timing, or clocking., information necessary to run such functions of the engine as fuel injection and spark plug firing. But those targets designed exclusively with tooth-to-slot transitions at regular intervals and with slot-to-tooth transitions at regular intervals, i.e. regular tooth and slot features throughout the target circumference do not contain any information that would indicate absolute position of the target.
Typically therefore, feature, i.e. teeth and slot, widths are lengthened and/or shortened to yield a xe2x80x9csignaturexe2x80x9d or coded pulse that can be distinguished as being different from the rest of the features, and this one signature pulse will yield information that will indicate absolute position of mechanical components, eg. of the engine. Determining the absolute engine position at start up is commonly referred to as xe2x80x9csynchronizationxe2x80x9d. To xe2x80x9csynchronizexe2x80x9d as quickly as possible, i.e. before a complete revolution of the target, additional xe2x80x9csignaturexe2x80x9d pulse generating features must be added to yield information at more than one place on the target. This is the method by which the internal combustion engine controller determines the absolute position of the pistons within the cylinders, thereby yielding information that can be utilized at startup of the engine to xe2x80x9csynchronizexe2x80x9d its functions and increase engine efficiency and decrease fuel emissions.
However, by eliminating the regularity of teeth or slots to gain the encoded signal, the regular timing pulse is adversely affected. By creating irregular or missing elements within the timing sequence, less timing information is provided. Also, because the feature transitions are not regular, magnetic fringing effects which decrease the accuracy and repeatability of sensor output, can arise.
Another desired feature is to be able to detect direction of target movement. One known technique is to utilize a differential sensor which will yield a certain pulse train, or signal, when the target is rotated in one direction and the inversion of that signal when the target is rotated in the opposite direction; with a regular target with wide features of one type and narrow features of the other type, for example, wide slots and narrow teeth. When the target is spinning in one direction the digital output will be high a majority of the time and when the target is spinning in the opposite direction, the digital output will be low a majority of the time; hence duty cycle of the output can be used to determine the direction of target rotation. However, when utilizing this technique a regular type of target does not contain any information with regard to absolute position and will not allow for xe2x80x9csynchronizationxe2x80x9d.
To provide a constant pulse train for timing purposes and an encoded pulse train for absolute engine position and directional information during startup, one could use two sensors and two separate targets, however, this would increase the expense to the automotive manufacturer and is therefore undesirable.
Therefore, there exists a need for a target and sensor system which allows the user the ability to determine both regular timing pulses and direction of target movement very quickly without sacrificing xe2x80x9csynchronizationxe2x80x9d performance, while being economical to use
It is an object of the present invention is to provide more information from a single sensing apparatus while utilizing the same target footprint.
It is another object of the present invention to provide a timing pulse train, and an encoded pulse train for determination of engine position, by applying multiple thresholds to the output of a single sensor which is detecting a target, or targets, designed to have multiple topographies without sacrifice of the constant, or regular timing pulses.
It is a further object of the present invention to provide a method and apparatus whereby a constant timing pulse and a variable encoded pulse may be gained from a single target by utilizing multiple thresholds on the output of a single magnetic sensing apparatus in order to yield a constant timing signal and special positional information for a mechanical apparatus. Several embodiments are disclosed which will yield this result.
It is a further object of the present invention to determine direction of target movement without reduction of encoding or timing information features on the target.